In a principal aspect, the present invention relates to a method and apparatus for constructing a support pier comprised of one or more compacted lifts of aggregate material. The apparatus enables formation or construction of a single or multi-lift pier within a soil matrix while simultaneously reinforcing the soil adjacent the pier. The apparatus thus forms a cavity in the soil matrix by forcing a hollow tube device into the soil matrix followed by raising the tube device, releasing or injecting aggregate through the tube device into the cavity section beneath the raised tube device and then for multi-lift piers driving, pushing, lowering, and/or forcing, the tube device downward to compact the released aggregate material while simultaneously forcing the aggregate material vertically downward and laterally outward into the surrounding soil matrix.
In U.S. Pat. No. 5,249,892, incorporated herewith by reference, a method and apparatus are disclosed for constructing short aggregate piers in situ. The process includes drilling a cavity in a soil matrix and then introducing and compacting successive layers or lifts of aggregate material in the cavity to form a pier that can provide support for a structure. Such piers are made by first drilling a hole or cavity in a soil matrix, then removing the drill, then placing a relatively small, discrete layer of aggregate in the cavity, and then ramming or tamping the layer of aggregate in the cavity with a mechanical tamper. The mechanical tamper is typically removed after each layer is compacted, and additional aggregate is then placed in the cavity for forming the next compacted layer or lift. The lifts or layers of aggregate, which are compacted during the pier forming process, typically have a diameter of 2 to 3 feet and a vertical rise of about 12 inches.
This apparatus and process produce a stiff and effective stabilizing column or pier useful for the support of a structure. However this method of pier construction has a limitation in terms of the depth at which the pier forming process can be accomplished economically, and the speed with which the process can be conducted. Another limitation is that in certain types of soils, especially sand soils, cave-ins occur during the cavity drilling or forming process and may require the use of a temporary casing such as a steel pipe casing. Use of a temporary steel casing significantly slows pier production and therefore increases the cost of producing piers. Thus, typically the process described in U.S. Pat. No. 5,249,892 is limited to forming piers in limited types of soil at depths generally no greater than approximately 25 feet.
As a result, there has developed a need for a unique pier construction process and associated special mechanical apparatus which can be successfully and economically utilized to form or construct aggregate piers at greater depths, at greater speeds of installation, and in sands or other soils that collapse and are unstable when drilled, without the need for a temporary casing, yet having the attributes and benefits associated with the short aggregate pier method, apparatus, and construction disclosed in U.S. Pat. No. 5,249,892, as well as additional benefits.